Rod-igniters for ramjet burners



Feb. 21, 1961 J. w. MULLEN, 1|

ROD-IGNITERS FOR RAMJET BURNERS Filed Sept. 25; 1954 FIG. 7.

MAIN FUEL SUPPLY PILOT FUEL SUPPLY PILOT AIR SUPPLY AIR FOR MAIN IBURNER MAIN FUEL SUPPLY m A N m mu mm AB FIG. 2.

7 JAMES M MULLEN I INVENTOR ATTORNEYS United States Patent fROD-IGNI'I'ERS FOR RAMJET BURNERS James W. Mullen II, Richmond, Va.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Navy Filed Sept. 23, 1954, Ser. No.458,034

2 Claims. (Cl. Gil-39.82)

The present invention relates to a combustion chamber flame igniter.More specifically, it relates to an improved flame igniter, of simpleand lightweight construction, for use in the combustion chamber of aramjet engine.

This application is a continuation-in-part of application Serial Number121,101, for Rod Igniters for Ramjet Burners, filed October 13, 1949,now abandoned.

The flame igniter is an extremely important component of a ramjetengine, since, as has been well established, proper ignition of theair-fuel mixture injected into the combustion chamber of the engine musttake place in order to obtain smooth burning and therefore a highcombustion efliciency along with a large developed output thrust.

In order to achieve proper ignition of a combustible fuel in acombustion chamber, it is esential that an igniting flame be spread oversubstantially the full cross-sectional area of the chamber in a mannerthat will allow symmetrical burning of a homogeneous air-fuel mixture.Prior art methods of achieving symmetrical burning include the use offlame holders constituted by arrayed radial gutters, grids, etc. which,though comparatively successful, are nevertheless large and complex. Asa result, badly needed space is occupied and unnecessary weight is addedto the vehicle in which the engine is mounted.

It is therefore one object of the present invention to provide a meansfor improving burning in the combustion chamber of a ramjet engine.

Another object of this invention is to provide a flame igniter foreffectively igniting a combustible mixture contained in a combustionchamber, over the entire crosssectional area of the chamber.

A further object of the present invention is to provide an igniter ofsimple and lightweight construction which will permit simplification ofthe structure of a ramjet engine combustion chamber.

Other objects and many of the attendant advantages of this inventionwill be appreciated readily as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing, wherein:

Fig. 1 is a perspective view, partly in axial section, of the combustionchamber of a ramjet engine showing the rod igniter which is the subjectof the present invention, and illustrating a pilot burner havingportions thereof broken away to reveal fuel injection and ignitionmeans; and

Fig. 2 is a View similar to Fig. 1, but showing a modification of theinvention and in which the pilot burner comprises a pyrotechnic flare.

Reference is first made to Fig. 1, where a combustion chamber 2 of aramjet engine is shown, together with a pilot burner and rod ignitersconstructed in accordance with the present invention. The ramjet engineconventionally comprises a duct having a diffuser inlet at its forward2,972,231 Patented Feb. 21, 1961 end and an exhaust nozzle at itsdownstream end. The intermediate portion of the duct serves as thecombustion chamber where fuel and air are intermixed and ignited toproduce a mass of hot gases which are expelled through the exhaustnozzle thereby delivering thrust. Only the intermediate portion of theduct which comprises the combustion chamber is illustrated, at 2, in thedrawing, since the showing of that portion alone is sufficient for anunderstanding of the present invention.

The pilot burner shown generally at 3 comprises a cylindrical housing 4flaring downstream into a frusto conical skirt 5. The pilot burner 3 issuspended within the combustion chamber 2 by pipes 6, 7 which mayconveniently serve as conduits from air or fuel sources (not shown) tothe housing 4, terminating therewithin in suitable nozzles 8, and 9. Ifso desired, an aperture as at 11 may be provided at the upstream end ofthe housing 4 to admit air to said housing for pilot flame combustion.The necessity for providing a separate pilot air supply can thereby beeliminated.

The fuel for the pilot flame may consist of hydrogen gas or othersuitable fuel which has the satisfactory burning characteristics ofrapid flame propagation and sustained combustion over a wide range ofair-fuel mixture ratios. The pilot fuel is injected into the housing 4where a combustible air-fuel mixture is created. A spark plug 12 ignitesthe combustible mixture injected into the housing, while the flaredskirt 5 serves to stabilize the flame against extinguishment by pressuresurges in the combustion chamber 2.

The rod igniters, which constitute the present invention, comprise aplurality of radially extending, preferably cylindrical rods 14. Therods are firmly secured at their outer ends to the wall of thecombustion chamber and extend transversely thereto substantially in theplane of the open end of the skirt 5.

In Fig. 2, there is illustrated a modification of the apparatus shown inFig. 1. The rod igniters 114 shown in Fig. 2 are similar in constructionexcept that said rods are arranged to extend inwardly of the skirt 5toward the axis of the combustion chamber 2. Also, in the Fig. 2structure the pilot burner including the fuel supply and ignition meansof Fig. 1 are shown as having been replaced by a pyrotechnic flare 15.It will be understood, however, that since both the pilot burner 3 andpilot flare 15 interchangeably serve the same purpose, it is notintended to limit either form of the invention to the specific pilotshown. Of course, when a flare is used, pipes 6 and 7 may be replaced bysupporting rods 17.

It will now be understood that fuel for main burner consumption isconveyed from the main fuel supply (not shown) to the combustion chamber2 by a pipe 18 terminating in a circular perforated conduit serving asthe main fuel injector 19. The fuel, generally a liquid hydrocarbon, isconveyed from the supply to the combustion chamber under high pressureso that the injector 19 efliciently atomizes the fuel. Followinginjection the atomized fuel rapidly combines with air moving through thechamber 2 at high velocity to form a homogeneous air-fuel mixture forcombustion. The combustible mixture is swept downstream from theinjector past the pilot burner and rod igniter by the force of theinrushing air. In the immediate region of the pilot burner and rodigniter, the mixture is ignited by the combined effect of the pilotflame and said rod igniter.

Though the exact mode of operation of rods 14 in the system is notcertain, it is believed that they serve to initiate or hold flamefronts, which have angles of spread that are substantially larger thanany heretofore attainable, and that bring about complete combustion in amuch'wshorteretime' than has. been. previously. possible. By use of thepresent rod igniters it is therefore possible, not only to simplifygreatly the construction of the combustion chamber itself, but also toutilize "a much shorter-tailpipe; thereby effecting a further saving inweight and size ofithevehicle'in TVvhlCh the igniter is mounted.

Obviously many modificationsand variations; of the present invention arepossible'inthe light of the above teachings. It is therefore'tobeunderstood that within thescope of the appended claims the inventionmay be practiced otherwise than'as specifically described.

What is claimed is:

LA-burner, assembly comprising a duct, means to supply'fuel'to said'duct, ahousing within said duct downstream-from said means, saidhousing-being outwardly:flared to'an opening atits downstream end andbeinig substantially closed at its usptream end, :means producing apilot flame within said housing, and a pin-r rality of substantiallyradially extending rods connecting the'said downstream end of thehousing to the inner wall of said duct, and located substantially in theplane of said downstream end out of the path of the pilot flame and inthe pathtof a combustible stream moving downstream in theduct forproducing expanded flame fronts and smooth, even burning ofthecombustible' prising a plurality of: substantially radially Yextending rods" connecting the flared downstreamendof-"the'housingto thewall of the duct, whereby substantially the entire combustible. streamflows between. said"rods,:said rods producing eddies resultingtinexpanded flame fronts so that smooth, even coinbustion'of thecombustible stream occurs. 7

References Cited in the file of this patent UNITED STATES PATENTS2,385;833 Nahigyan Oct.---2, 1945 2,622,396 Clarke et a1. Dem 23, 1952 12,625,795 Brzozowski Jan. 20, 1953" 2,632,300 Brzozowski Mar-.= 24, 19532,640,321 Po-uchot' June 2,4953 2,780,916 Collins Feb: 12, 1957

